1. Field of the Invention
The present invention relates to a wafer prober which tests the electrical characteristics of a wafer chip.
2. Description of the Related Art
Generally, when the electrical characteristics of a wafer chip are tested, respective probes contact a plurality of microscopic electrode pads on a chip and the electrical test is performed through these probes. These contacting operations from the initiation to the termination of the test in the conventional wafer prober are shown in FIGS. 5 A to 5 D.
At first, as shown in FIG. 5 A, a probe 1 is brought close to an electrode pad 2 made of aluminium disposed on a wafer chip 3. Internal aluminium wiring 4 is disposed on the wafer chip 3 near the electrode pad 2. Subsequently, as shown in FIG. 5 B, the probe 1 is brought into contact with the electrode pad 2 under a specified pressure. At this time, the surface of the electrode pad 2 is scraped to some extent by the tip of the probe 1 because of the pressure applied to the probe 1 and the elasticity of the probe 1. Therefore, waste aluminium 5 scraped from the electrode pad 2 is left around the tip of the probe 1.
Under these conditions, an electrical test for the wafer chip 3 is performed by a testing device (not shown) through the probe 1. When the test is completed, the probe 1 is separated from the electrode pad 2 on the wafer chip 3, as shown in FIG. 5 C. However, the waste aluminium 5 left around the tip is scattered all around because of the elasticity of the probe 1. As a result, a gap between the electrode pad 2 on the wafer chip 3 and the internal aluminium wiring 4 next to the electrode pad 2 is sometimes jammed with the waste aluminium 5. Furthermore, as shown in FIG. 5 D, when the probe 1 is moved from the wafer chip 3 in order to test the next chip after completion of the testing the previous chip 3, the waste aluminium 5 attached to the tip of the probe 1 sometimes falls into the gap between the electrode pad 2 and the internal aluminium wiring 4.
The gaps between the internal aluminium wirings 4 are extremely narrow as a result of the progress in the miniaturization of the semiconductor device. Consequently, the electrode pad 2 is easily short-circuited by the internal aluminium wiring 4 when the gap between the electrode pad 2 and the internal aluminium wiring 4 is jammed with the waste aluminium 5, as above described. As a result, there is a problem in that there is an increase in the number of chips which are judged to be inferior by the test and the yield therefore decreases. Furthermore, some chips which are judged to be satisfactory and, therefore, covered with a glass coating or resin molded as finished goods, are contaminated by the waste aluminium 5 and subsequently fail.